Lecture 12.2: User-Enabled Device Authentication II CS 436/636/736 Spring 2012 Nitesh Saxena.

Lecture 12.2: User-Enabled Device Authentication II

CS 436/636/736

Spring 2012

Nitesh Saxena

Course Admin

• HW3 graded• Solution provided• Stats to be posted

• HW4 Posted • Problem 1 and 2: due Apr 26, 11am

(individually assigned)• Problem 3: demo due 11am May 7 (can be

teams of 2)• Please sign-up for demo slots – sheet being

circulated

Course Admin

Final Exam – May 3 (Thursday) 10:45 to 1:15 Venue – CH 430 (our regular lecture room)

Covers everything (cumulative) 35% -- pre mid-term material 65% -- post mid-term material

Again, close-book, just like the mid-term Exam Review on May 1

Challenges

OOB channels are low-bandwidth!OOB channels are low-bandwidth! One of the device might not have a One of the device might not have a

receiver!receiver! Neither has a receiver and only one has Neither has a receiver and only one has

a good quality transmittera good quality transmitter (Non-)Universality!(Non-)Universality!

Comparative Usability! Multiple devices -- scalabilityMultiple devices -- scalability

Many Mechanisms Exist

See survey: [Kumar, et al. @ Percom’09] Manual Comparison or Transfer:

Numbers [Uzun, et al. @ USEC’06] Spoken/Displayed Phrases: Loud & Clear [Goodrich, et al. @

ICDCS’06] Images: [Goldberg’96][Perrig-Song’99][Ellison-Dohrman @

TISSEC’03] Button-enabled data transfer (BEDA) [Soriente, et al. @ IWSSI’07] Synchronized Patterns [Saxena et al. @ ACNS’08 & SOUPS’08]

Automated: Seeing-is-Believing (SiB) [McCune, et al. @ S&P’05] Blinking Lights [Saxena, et al. @ S&P’06] Audio Transfer [Soriente, et al. @ ISC’08]

5

A Comparative Usability Study

How do these mechanisms compare with one another in terms of usability? Timing; error rates; user preferences

Needed a formal usability study

Automated testing framework 20 participants; over a 2 month long period

Surprise: Users don’t like automated methods: handling

cameras not easy

TESTED METHODS (1/5)

Number Comparison “65473” =? “75853”

Phrase Comparison “Alice buys jackets” =? “John likes elephants”

Image Comparison

=?

TESTED METHODS (2/5)

Audiovisual synchronization methods Beep-Blink

.. … .. …

Blink-Blink

… … … …

Button enabled (BEDA) methods LED-Button

Vibrate-Button

Button-Button

TESTED METHODS (3/5)

TESTED METHODS (4/5)

Loud and Clear (L&C) variants Speaker-Speaker

=?

Display-Speaker

=?

John buys a

car

John buys a

car

John buys a

car

John buys a car

TESTED METHODS (5/5)

Seeing is Believing (SiB)

Blinking Lights

… … …..

HAPADEP Variant

Comparative Usability Study: Time

Comparative Usability Study: Ease-of-Use

Cluster Analysis: Big Picture!

Conclusions from the study Both devices have a display

Numeric Comparison One device does not have a display but an audio interface

L&C Display-Speaker if one has a display and the other has a speaker

Audio Transfer if microphone is available on one, and speaker on the other

Interface constraint device(s) BEDA Vibrate-Button, if possible BEDA LED-Button otherwise

Challenges

OOB channels are low-bandwidth!OOB channels are low-bandwidth! One of the device might not have a One of the device might not have a

receiver!receiver! Neither has a receiver and only one has Neither has a receiver and only one has

a good quality transmittera good quality transmitter (Non-)Universality!(Non-)Universality!

Usability!Usability! Multiple devices – scalability

Secure Group Association

Small groups (> 2) of users + devices phones, PDAs, laptops

Common use-cases: Share content as part

of an ad hoc meeting Multiplayer games Multimedia streaming

Two user tasks: Comparison of SAS strings Verification of group size

18

SAS-based Group Key Agreement

Ui G : BD GKA

Ste

p 1

:S

tep 2

:K

ey

Com

pu

tati

on

Ui

G :

12

21

11)(

][ 121

ini

ni

nsi

ssssi

XXXPK

gKi

n

isi gPK

is

i

ii PK

PKX

1

1

Authenticate PKi using SAS protocol

Broadcast SAS value being xor of Ri values

Ste

p 1

:S

tep

2:

Key

Com

pu

tati

on

Authenticate Xi using SAS protocol

Broadcast SAS value being xor of Ri values

12

21

11)(

][ 121

ini

ni

nsi

ssssi

XXXPK

gKi

n

Usability Evaluation of Group Methods Usability evaluation of FIVE simple

methods geared for small groups (4-6 members)

Three leader-based

&

Two peer-based

20

Study Goals

How well do users perform the two tasks when multiple devices and users are involved:

Comparison/Transfer of SAS strings?

Counting number of group members?

21

Leader-Based Methods (1/3)

Leader-VerifySize-VerifySAS (L-VS-VS): Leader announces 5-digit SAS, group members verify the displayed SAS and the group size.

22

1. Enter the group size: 42. Announce the

verification code: 397153. Accept or Reject

1. Group size is: 4,

verification code is: 397152. Accept or Reject

The Verification Code is: 39715

Leader-Based Methods (2/3)

Leader-VerifySize-CopySAS (L-VS-CS): Leader announces SAS, members enter it to their devices and verify group size.

23

1. Enter the group size: 42. Announce the

verification code: 397153. Accept or Reject

1. Enter verification code: 39715

2. Group Size is: 42. Accept or Reject

The Verification Code is: 39715

Leader-Based Methods (3/3)

Leader-VerifySize-AudioSAS (L-VS-AS): Leader’s device broadcasts SAS (over audio), other devices record & verify. Users only verify group size.

24

1. Enter the group size: 43. Accept or Reject

1. Group Size is: 42. Accept or Reject

Peer-Based Methods (1/2)

Peer-VerifySize-VerifySAS (P-VS-VS): Each peer verifies group size and compares SAS with left-hand peer.

25

1. Your code is: 39715Does it match with the code of the person next to you?2. Group size is: 43. Accept or Reject

Wh

at is

you

r co

de?

My

cod

e is

39

71

5

Wh

at is your co

de?

My co

de is 3

97

15

What is your code?

My code is 39715

What is your code?

My code is 39715

Peer-Based Methods (2/2)

Peer-InputSize-VerifySAS (P-IS-VS): Each peer enters group size and compares SAS with left-hand peer.

26

1. Enter Group Size: 42. Your code is: 39715Does it match with the code of the person next to you?3. Accept or Reject

Wha

t is

your

cod

e?

My

cod

e is

397

15

What is your code?

My cod

e is 39715

What is your code?

My code is 39715

What is your code?

My code is 39715

Usability Testing Details

64 Participants 7 four-person groups 6 six-person groups

Nokia smart phones communicating over Wi-Fi Test Cases:

Normal Simulated Insertion Attack Simulated Evil-Twin Attack

User Feedback SUS questionnaire (system usability scale) Additional perception of security question

27

Test Results (Normal Case)

28

Test Results (Attack Cases)

29

Combined Usability Metrics

30

Better

• Interesting result: peer based methods performed better in general

Summary of results

Peer-based methods generally better than Leader-based ones

P-IS-VS has the best overall usability L-VS-CS has the worst L-VS-VS and L-VS-AS are natural choices if

peer-based methods are not suitable L-VS-VS > L-VS-AS

Over-counting unlikely in small groups Entering group size is better than verifying it

31

Other open questions

Rushing user behavior (Saxena-Uddin [ACNS’09])

Hawthorne effect Security priming More usability tests

References

Many of them on my publications page